Method of casting a diffuser element

ABSTRACT

A DIFFUSER ELEMENT OF THE TYPE USED IN A HIGH PERFORMANCE EVACUATION SYSTEM AS WELL AS THE METHOD FOR FABRICATING THE DIFFUSER IS PROVIDED. A PRECISELY MACHINED TWO PART TAPERED MANDREL IS ACCURATELY POSITIONED WITHIN A HOLLOW CASING. A SUITABLE MATERIAL THAT IS POURABLE AND WHICH HARDENS AFTER A PERIOD OF TIME IS THEN INTRODUCED INTO THE ANNULAR CHAMBER DEFINED BY THE OUTSIDE DIAMETER OF THE MANDREL AND THE INSIDE DIAMETER OF THE CASING. AFTER THE POURED MATERIAL HARDENS, THE MANDREL SECTIONS ARE SEPARATED AND AXIALLY REMOVED. THE COMBINATION OF THE HARDENED MATERIAL AND THE CASING FORM THE DIFFUSER ELEMENT.

29, 1972 c. JENNINGS 3,645,15

METHOD OF CASTING A DIFFUSER ELEMENT Filed April 16l 1970 5 Sheets-Sheet l ZP/lv; 7,45 PLAS rfc T lql- INvE T R ffy/N@ NAM/g5 ATTOR EYS b 29, 1972 l. c. JENNINGS METHOD OF CASTING A DIFFUSER ELEMENT 5 SheetSSheet 2 Filed April 16( 1970 ATT NEYS Feb. 29, 1972 l. c. JENNINGS METHOD OF CASTING A DIFFUSER ELEMENT 5 Sheets-Sheet 5 Filed April 16 1970 Feb. 29, l972 1. c. JENNINGS METHOD OF CASTING A DIFFUSER ELEMENT 5 Sheets-Sheet 4 Filed April 16 1970 93M@ @wir ATT RNEYS Feb' 29 1972 1. c. JENNINGS 3,64

METHOD OF CASTING A DIFFUSER ELEMENT Filed April 16 1970 5 Sheets-Sheet 5 RWEYS 3,646,185 ME'IHD GF CASTING A DIFFUSIER ELEMENT Irving C. Jennings, The Nash Engineering Co., South Norwalk, Conn.

Continnation-in-part of abandoned application Ser. No.

622,665, l/Iar. 13, 1967. This application Apr. 16, 1970,

Ser. No. 29,251

Int. Cl. B29c 17/12; 328i) 7/28 U.S. Cl. 264-161 15 Claims ABSTRACT F THE DISCLSURE A diffuser element of the type used in a high performance evacuation system as well as the method for fabricating the diffuser is provided. A precisely machined two part tapered mandrel is accurately positioned within a hollow casing. A suitable material that is pourable and which hardens after a period of time is then introduced into the annular chamber defined by the outside diameter of the mandrel and the inside diameter of the casing. After the poured material hardens, the mandrel sections are separated and axially removed. The combination of the hardened material and the casing form the diffuser element.

This application is a continuation-impart application of Ser. No. 622,665, filed Mar. l3, 1967, and now abandoned.

This invention relates generally to diffuser elements such as used in a vacuum inducing system and more particularly to an improved diffuser and an improved method for manufacturing the diffuser.

The supersonic jet diffuser forming a part of this invention is of the type that is utilized with the vacuum producing apparatus described in U.S. Pat. No. 3,064,878 granted on Nov. 20, 1962 to William H. Bayles et al. Briefly, the supersonic jet diffuser develops its optimum, vacuum inducing performance only when utilizing supersonic ow. Consequently, for a high performance evacuation system the supersonic jet diffuser is available in the system but is not effectively cut in until the Vacuum has reached predetermined conditions. The jet diffuser includes a chamber that supports the supersonic ow by combining a primary and secondary fiuid stream. The streams are mixed in a predetermined passage and decelerated in order to increase the pressure of the system and decrease the jet diffuser fluid tiow velocity. This action reduces the effort or work required to operate the evacuator or vacuum pump.

It is essential that the internal bore dimensions of the diffuser be very accurate. The prior art method of forming the diffuser was to first bore a hole axially through a solid bar then taper the bore. Machining of the diffusers was Very slow due to the small bores required. Another factor contributing to manufacturing difficulties and hence high costs is the long overhang of the boring tools.

The present invention provides an improved diffuser by means of a novel fabricating method. The outside surface of a multisection, stainless steel mandrel is machined to the exact internal dimensions required of the diffuser. The mandrel is centralized in a casing to define an annular chamber between the outside dimension of the mandrel and the inside dimension of the casing. In the embodiments illustrated the elongated mandrel is machined with oppositely angled tapers at the ends thereof and a central section that is circular in cross section.

In one embodiment of the invention, a suitable plastic material, such as Devcon B Plastic Steel that is chemically inert and has desirable shrink rate characteristics is introduced into the annular chamber and then cured. After 3,5%35 Patented Feb. 29, i972 the plastic filler material has cured, for example by any well known technique that is compatible with the materials characteristics, the mandrel sections are separated and are removed axially. This leaves only the finished diffuser comprising an external casing and a hollow plastic-like insert having an internal tapered bore conforming to the external shape of the mandrel. No further machining is required on the bore of the diffuser. From the foregoing description it will be evident that a low cost diffuser can be made by utilizing the various steps of the method to be described hereinafter Accordingly, it is an object of this invention to provide an improved, diffuser for use in a high performance evacuation system.

It is another object of this invention to provide an improved method for fabricating a diffuser element as described above.

It is another object of this invention to provide a method for forming a diffuser that does not require subsequent machining on the bore thereof.

It is a particular object of this invention to provide a method of forming a diffuser element that utilizes a multisection, removable mandrel in combination with a hollow casing.

A feature of this invention is that diffusers .may be very accurately fabricated at low cost and without conventional machining techniques.

A further object of this invention is to pro'vide a diffuser comprised of an external shell having an integral moldable insert provided with a tapered bore.

These and other features, objects and advantages of the invention will in part be pointed out with particularity and will in part become obvious from the following more detailed description taken in conjunction with the accompanying drawings which form an integral part thereof. In the various figures of the drawing like reference characters designate ylike parts.

In the drawing:

FIG. l is a fragmentary elevational view of a pump and supersonic jet diffuser combination employing the present invention;

FIG. 2 is a sectional elevational view of the ejector pump used in FIG. l and which includes a diffuser member fabricated by the method of this invention;

FIG. 3 is an inverted elevational View of the diffuser member alone;

FIG. 4 is an elevational view, partly in section, illustr-ating the molding apparatus used to form the diffuser element;

FIG. 4A is a sectional plan view taken along line lA-4A of FIG. 4;

FIG. 5 is a sectional, elevational view of an alternative embodiment of this invention;

FIG. 6 is an inverted elevational view of the alternative diffuser element by itself;

FIG. 7 is an elevational View, partly in section, showing the molding apparatus used to form the diffuser of FIG. 6;

FIG. 7A is a plan View of the apparatus shown in FIG. 7;

FIG. 8 is an elevational view of still another alternative embodiment, partly in section, of the diffuser element;

FIG. 9 is a plan view taken along line 9 9 of FIG. 8;

FIG. l() is an elevational view, partly in section, illustrating the apparatus used to mold the member shown in FIG. 8;

PIG. ll is a plan view taken along line 11-11 of FIG. l0; and

FIG. l2 is a schematic illustration of the steps comprising the method of this invention.

spaeter A typical system that employs the product of this invention is shown schematically in FIG. l. The following description is given for purposes of illustration only in order to establish the environment of the present invention. For a complete description of the system, reference may be had to the above mentioned Bayles et al. patent.

A standard two stage vacuum pump 2u includes two pumps 22 (only one shown) of the hydroturbine type connected in series with one another. Each of the pumps is of the type disclosed for example in US. Pats. No. 1,718,294 and 1,797,980. The two pumps are mounted upon a common chassis in axial alignment and are driven by a common motor. Reference may be had to the patents referred to above for a more complete disclosure of the pump structure, and no detailed description will be given herein. The vacuum pump details are not broadly' of importance since useful application of the principle of the invention can be made with any suitable evacuator or vacuum pump.

A cold water main supplies water to the two pumps. An intake conduit 31B is connected to the intake side of the rst pump. A conduit 32 connects the output of the first pump to the input of the second pump. The second pump discharges to a conduit 34. A supersonic jet diffuser 36 connected to the intake end of the conduit 3i) receives irnotive air through a conduit 33. The conduit 3S may communicate with the atmosphere through a manually operable valve 4l?, a motive fluid intake conduit 42 and an air filter 44. A conduit 46, equipped with a vacuum gauge 4S communicates at one end with the chamber or system under evacuation (not shown), and at the other end with the suction of the ejector 3S through a side inlet passage. For purposes of clarity, in FlG. 2 nonessential elements have been omitted. It will be seen then that the diiuser element 36 is threadably secured in one end of body member (ail which is provided with a threaded aperture 62 arranged to receive conduit du. Another threaded aperture 64 receives conduit 33. A nozzle 66 is adjustably secured within the body member 60 in opposition` to one end of the diffuser element. The functioning of nozzle 66 may be fully understood by reference to the Bayles et al. patent.

Referring now particularly to FIG. 2, it will he seen that in this embodiment diffuser element 36 is comprised of an elongated cylindrical member 7G having external threads 72 and 7d formed at the ends thereof. A plastic type insert 76 is integral with the elongated sleeve 7 d and includes a lirst, convergently tapered bore 7S extending downwardly approximately one-third of the length or" the diffuser, a uniform bore Si? in the central portion of the diffuser and a divergent bore 82 which occupies the remainder of the length of the diffuser. When the diluser is properly seated within the body member 6@ a shoulder 84 of the diffuser is seated in a recess Se in member 69 and a piloting diameter SS of the diiluser is disposed within bore 9G of the body member.

Referring now to FIGS. 3, 4 and 4A, the apparatus to mold the diffuser element 36 will now be described. lt should be noted that while the structure shown in FlG. 2 is oriented properly with respect to the system shown in FIG. l, the external View of the diffuser as shown in FlG. 3 is inverted 180 degrees in order to conform to the molding apparatus shown in FIG. 4.

A two piece mandrel 199 is used to provide the internal bore configuration of the diffuser element. A rst tapered section 192 is very accurately machined to the dimensions required by section 82. The second central part of the mandrel is provided with a portion 1M that is cylindrical in cross section and is accurately machined to provide the dimensions of bore 80 and a third tapered section of the mondrel 106 is accurately machined to the dimensions of bore 78. Sections 1de and 166 are made in one piece and includes an axially extending piloti 1Gb that is adapted to receive in Socket 110 of the first mandrel section.

CII

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The mandrel section 102 is permanently attached to a block 112, which is provided with a centralized opening 114 to receive the threaded end 72 of casing 70. In this manner the mandrel and the casing are concentrically mounted with respect to each other and in such a manner that an annular chamber 119 is provided between the outside diameter of the mandrel and the inside diameter of the casing. Block 124i at the lower end of the molding apparatus has a seat 122 arranged to receive the lower threaded end 7d of casing 'itl and a concentrically positioned smaller aperture 124 arranged to receive the lower end 126 of mandrel section 1196. Upper and lower end plates 132 and 134 complete the apparatus. The end plates are connected by means of tie rods 13b, the lower threaded ends 137 of which are engaged in plate 134, the upper ends ot which are retained by nuts 138.

Block 112 is provided with an aperture 140 that communicates with the annular chamber 119 in order to permit introduction of the material that forms the insert member. A second aperture 142 in block 112 is used for venting purposes. It should be noted that end plate 132 is provided with apertures 144 and 146 that are in registry with apertures 146 and 142 respectively.

ln order to fabricate the diffuser, the mandrel is initially coated with a mold release agent so that the plastic or moldable material will not stick to the mandrel. The rnoldable material utilized may be chosen from a number of suitable materials. ln this connection, Devcon B Plastic Steel may be used, which is a trademark of the Devcon Corp., Danvers, Mass. and constitutes steel particles, 20% fluid epoxy resin and a catalyst. Another material which may be eiectively used is Cerromatrix, a trademark of Cerro Be Pasco Corp. and which is a controlled shrinkage bismuth alloy constituted of 48% bismuth, 14.5% tin, 28.5% lead and 9% antimony that expands on cooling. Other materials that may be utilized as the selected moldable material in order to make the present diiuser may be a polyester hardening material that takes the form of a powder that is injected and hardened by heating. Moreover, it is possible to use a low temperature melting material-like type metal, such as antimonial lead or zinc as the selected moldable material. The plastic material which may be Devcon B Plastic Steel or other suitable material can be poured into the chamber through registered apertures 144 and 149, or it can be injected by any conventional manner well known in the art. The mixture is then cured by known techniques to provide a plastic insert member 76 having the desired internal taper configuration. When this is accomplished a tool such as an endrnill is run through registered apertures 144, 14.0 and 146, 142 in order to remove the gate and vent. The mandrel is then stripped from the mold by means of nuts 128 and 130. The mandrel is removed by axially moving the two sections in opposite directions. It will be apparent then that no internal machining is required since the tapered bore is a function of the accurately machined mandrel.

Referring once again to FIG. 3 diameter portions 88 and 152 are obtained during the molding process by seat 154 in block and the combination of bore 156 and the enlarged end of the mandrel. It should also be noted that radius 15S at the end of bore 78 of the diluser is obtained during the molding process from the radius 159 that is present at the juncture of section 106 and enlarged diameter 126 of the mandrel. For purposes of illustration only, the molding apparatus has been shown in the vertical position with the plastic-like material introduced from the top. The diiuser element shown in FIGJ` is also oriented in the same manner. However, the diifuscr assembly illustrated in FIG. 2 is oriented in the same manner as in FIG. l.

FIGS. 5, 6, 7 and 7A illustrate an alternative embodiment of the diffuser member together with alternative molding structure. Threaded connection means 160 and 162 as well as the nozzle 164 are again provided in hous ing 166. The diffuser assembly which will be described subsequently is secured to the housing by means of bolts 168. In this embodiment a cast shell 170 is utilized instead of the cylindrical pipe member of the previous embodiment. A flange 176 is formed at the bottom of the assembly and is also provided with mounting holes 178 so that the assembly may be installed in the evacuation system. Shell 170 is cast with a bore 180 that is somewhat larger than the desired diffuser bore in order to accommodate a plastic-like insert member 182. As in the previous embodiment, the insert member is formed with three continuous bores the first of which 184A is convergently tapered and extends approximately 1/s the length of the tube. The second bore 184B is of uniform diameter and is centrally located while the third bore 184C is divergent and is located at the bottom of the diffuser element. The extreme ends of the diffuser are in communication with appropriate conduits described in connection with the first embodiment.

Referring now particularly to FIG. 7 and FIG. 7A, it will be seen that mandrel 200 is comprised of a flrst section 202 that is tapered to the shape desired for the diffuser section 184C and includes an elongated central aperture 204. The second section of the mandrel has a portion 206 that is cylindrical in cross section in accordance with the straight bore 184B of the diffuser element and a contiguous portion 208, which is tapered in conformity with the opposite internal end 184A of the diffuser. Along its entire length the mandrel is smaller in diameter than comparable inside diameter sections of the core 170 in order to define an annular chamber 210. The upper end of the mandrel is provided un'th a piloting diameter 212 while the lower end of the mandrel includes two enlarged diameters 214 and 216. An upper plate 218, having a central opening 220, is positioned on the upper end of the mandrel and is accurately and concentrically located with respect thereto by means of dowel pins 222 that are integral with the upper plate and which is received in holes 178 in the flange portion 176 of the shell. Stripper bolts 224 are threadably engaged in the upper plate 218 and bear against the top surface of flange 176.

At the lower end of the assembly a plate 226 is positioned centrally in the annular chamber 210 by means of stripper bolts 228. Mandrel diameters 214 and 216 are concentrically positioned in central bore 230 and recess 232 of the bottom plate respectively. Finally, the mandrel sections are secured to each other by means of an elongated threaded rod 234 that is secured at one end of mandrel 206 and which extends through bore 204 of mandrel section 202. The threaded rod extends above plate 218 and is provided with a spacer 236 and a nut 238 in order to complete the assembly. Gasket 240 is also included between plate 218 and flange 176 of the diffuser shell.

The mandrel shown in FIG. 7 is centralized within the cast shell and is held in an accurately located position by means of bolts 228 and pins 222. The plastic-like moldable material is introduced through opening 241 and vented through opening 242, both of which are formed at the upper end of mandrel section 202. Both openings 241 and 242 are in communication with the annular chamber 210. The gate and vents may be removed by an endmill in the same manner as described in connection with the previous embodiment. After the moldable material has cured, the mandrel is stripped by means of bolts 224 and 228. The mandrel is removed by taking off nut 238 and pulling the mandrel axially in two opposite directions. No additional internal machining is required for the tapered diffuser bore which now has dimensions that are exactly the same as the outside configuration of the mandrel. The diffuser extension 244 is obtained during the molding process by virtue of the bore 230 in the lower plate. Means (not shown) for supporting end plates 218 and 226 in a manner functionally equivalent to that shown in FIG. 4 are also provided for the second embodiment of the molding apparatus.

Referring now to FIGS. 8 to 11, there is shown still another embodiment wherein standard pipe fittings are used for the diffuser shell in place of the casting and length of pipe shown in the previous embodiments. Once again, a two part mandrel 300 is used. The first section 302 is tapered and is provided with a central bore 304 that terminates at its lower end in an enlarged opening 306. The second section of the mandrel 308 is cylindrical in cross section and is provided with a piloting member 310 at its upper end that seats in opening 306. A pin 312 extends between and accurately positions the mandrel sections with respect to each other. The mandrel 308 is provided with two enlarged diameters 316 and 318 at the end thereof. The upper end of the first mandrel section is provided with a piloting diameter 320, a filling hole 322 and a vent hole 324.

An internally threaded flange 326 is secured to external threads of a pipe section 328 to form the upper end of the diffuser assembly. Similarly, an internally threaded flange 330 is secured to the external threads of a pipe section 332 to form a lower end of the diffuser assembly. The upper end of an internally threaded reducing coupling 334 is rigidly secured to the external threads at the lower end of pipe section 328 and is provided with a running fit at its lower end to slidably receive the upper end of pipe section 332. Completing the molding apparatus is a top plate 336 that is accurately located with respect to ange 326 by means of dowel pins 338. At the lower end of the assembly, a bottom plate 340 having a central bore 342 that mates with mandrel diameter 316 and a recess 344 that mates with mandrel diameter 318, is included. Stripper bolts 346 are threadably mounted in plate 336 and bear against the top surface of flange 326 while stripper bolts 348 are threadably disposed in plate 340 and have their ends disposed in flange 330 of the diffuser assembly. The molding apparatus is completed by rod 350 that is positioned in bore 304 of the flrst mandrel section and which is secured to the assembly by means of a spacer 352 and a wing nut 354. The pipe section 332 is unscrewed in the reducing bushing 334 until a gasket 356 is in contact between plate 336 and flange 326. The pipe 332 is further rotated until the dowel pin 338 drops in the nearest bolt hole in flange 326. This puts the bolt holes in flanges 326 and 330 in proper alignment and maintains a fixed distance between these flanges.

As in the previous embodiments, the plastic-like material is introduced through opening 322. Since the mandrel has a smaller outer diameter than the various components that comprise the shell, the plastic-like material, when cured, will then form an insert shown as 358 in FIG. 8. Because of the configuration of the mandrel it will be apparent that the resulting internal bore of the diffuser will have a rst convergently tapered portion 360A at the upper end thereof, a centralized cylindrical portion 360B and a lower divergently tapered portion 360C. The diffuser extension 362 results from flange 330 being spaced from the lower end of pipe section 332. Means (not shown) for supporting end plates 336 and 340 in a manner functionally equivalent to that shown in FIG. 4 are also provided for the third embodiment of the molding apparatus.

From the foregoing, it will be apparent that all of the objectives stated hereinabove have been met. A very accurately dimensioned diffuser assembly is provided at very low cost. It is no longer necessary to internally -bore the diffuser assembly to provide the elongated tapers that are necessary. Because this costly machining operation has been eliminated, diffuser assemblies may now be manufactured in much shorter times and at considerably less expense. The accuracy of the diffuser bore is increased over that of the prior art because of the ease with which the mandrel may be formed as compared with the necessity of the internal boring operations that were previously required. Various structure for forming different diffuser assemblies have been described.

What is claimed is:

1. A method for forming a diffuser assembly for use in a high performance evacuation system and having a converging-diverging nozzle, said method utilizing molding apparatus and comprising the steps of:

(a) providing a multi-section mandrel having the converging-diverging prole of the nozzle, said mandrel being removably jointed between the converging and diverging sections;

(b) substantially coaxially locating the mandrel within a casing to provide an annular chamber between the mandrel and the casing, said casing having ends supporting the mandrel and enclosing the chamber and providing openings communicating with the chamber;

(c) injecting a molding material with controlled low shrinkage through said openings to till said annular chamber;

(d) curing the molding material whereby an integral assembly of an insert member and a casing is formed, constituting the diffuser assembly; and

(e) boring out said openings through which said material has been introduced up to one end of said mandrel and disassembling and removing the latter from the casing without affecting the shape of the insert member.

2. The method in accordance with claim 1 wherein said step of forming the mandrel comprises the step of forming opposing tapers interconnected by an intermediate cylindrical section on the outer surface of said multi-section mandrel.

3. The method in accordance with claim 1 wherein said material is a mixture of powdered steel, iiuid epoxy resin and a catalyst therefor.

4. The method in accordance with claim 1 wherein the ends of the outer wall of said casing are provided with screw threads for initially holding the mandrel in the molding apparatus, and after the diffuser assembly is formed for screw-connecting said assembly into said evacuation system.

5. The method in accordance with claim 1 including the step of applying a mold release agent to the outer surface of the mandrel prior to injecting said material.

6. The method in accordance with claim 1 wherein the step of removing the mandrel from the casing comprises the step of axially displacing the mandrel sections in opposite directions.

7. The method in accordance with claim 1 wherein said material is a controlled shrinkage alloy constituted of bismuth, tin, lead and antimony, said material expanding on cooling.

8. The method in accordance with claim 1 wherein said material is a polyester hardening material in the form of an injectable powder that is hardened 'by heating.

9. The method in accordance with claim 1 wherein said material is a low temperature melting metal.

10. The method in accordance with claim 1 wherein said molding material is a Huid epoxy molding composition.

11. A method for forming a diluser assembly for use in a high performance evacuation system and having a converging-diverging nozzle, said method utilizing molding apparatus and comprising the steps of:

(A) providing a multi-section mandrel having the converging-diverging proiile of the nozzle, said mandrel being removably jointed between the converging and diverging sections,

(B) substantially coaxially locating the mandrel within a casing to provide an annular chamber between the mandrel and the casing said casing having ends supporting the mandrel, enclosinv the chamber, and providing openings communicating with the chamber,

(C) injecting a fluid epoxy molding composition through the openings to ll said annular chamber,

(D) curing the molding composition whereby an integral assembly of an insert member and a casing is formed, constituting the diffuser assembly; and

(E) boring out said openings through which said molding composition has been introduced by the one end of said mandrel and disassem-bling and removing the latter from the casing without affecting the shape of the insert member.

12. The method in accordance with claim 11 wherein said step of providing the mandrel comprises the step of forming opposing tapers interconnected by an intermediate cylindrical section on the outer surface of said multisection mandrel.

13. The method in accordance with claim 11 including the step of applying a mold release agent to the outer surface of the mandrel prior to injecting the moldable composition.

14. The method in accordance with claim 11 wherein the hardenable material is a mixture of powdered steel, fluid epoxy resin and a curing catalyst therefor.

15. The method in accordance with claim 11 wherein the ends of the outer wall of said casing are provided with screw threads for initially holding the mandrel in the molding apparatus, and after the diluser assembly is formed for screw-connecting said assembly into said evacuation system.

References Cited UNITED STATES PATENTS 683,862 10/1901 Petit 264-318 1,022,231 4/1912 Garey 249-173 1,580,518 4/1926 Martine 249-186` 1,598,059 8/1926 Cykler 249-184 2,937,421 5/1960 Taccone 264-313 3,318,563 5/ 1967 Downing 249-184 3,385,553 5/1968 Garey 249-175 ROBERT F. WHITE, Primary Examiner R. R. KUCIA, Assistant Examiner US. Cl. X.R. 

